Method of fluid bed roasting



Oct. 7, 1958 H. M. CYR ET AL METHOD OF FLUID BED ROASTING Filed Sept. 4,1956 INVENTOR HOWARD M. OYR TRAOEY F. STEELE 7 m, M, wwfl ATTORNEYSUnited States Patent T METHOD or FLUID BED ROASTING Howard M. Cyr andTracey F. Steele, Palmerton, Pa., assignors to The New Jersey ZincCompany, New York, N. Y., a corporation of New Jersey ApplicationSeptember 4, 1956, Serial No. 607 ,833

8.Claim's. (Cl. 7 59) This invention relates to the roasting of zincsufide or'e concentrates and, more particularly, to the separation ofcadmium and lead sulfide components, as well as other indigenousvolatile sulfide components, of zinc sulfide ore concentrates in thecourse of roasting these concentrates in a fluid bed operation.

In United States Letters Patent No. 2,621,118 there is described amethod of roasting zinc sulfide ore concentrates in a multi-bed fluidcolumn. Although this method is extremely effective insofar as roastingis concerned, the cadmium and lead components of the ore are largelyretained in the roasted product with the result that the cadmium andlead appear as impurities in the final zinc metal product obtained bysmelting the roasted ore. However, by using a combination of physicaland chemical controls to maintain separate but continguous volatilizingand roasting zones in the upper and lower portions, respectively, ofsuch a fluid column, one of 'us found that it was possible to obtain atleast about 90% elimination of the cadmium and lead components of a zincsulfide ore concentrate while the ore was being roasted. This expedientwas characterized by the fact that less than theory air was used forroasting so as to insure an upper fluid bed zone in which substantiallynonoxidizing conditions prevailed and further by the fact that the bedtemperature was maintained close to and preferably somewhat above 1100C. The use of less than theory roasting air was disadvantageous becauseit resulted in rather high residual sulfur contents in the calcine, andthe use of such high temperature generally required the adoption ofsintering-control expedients "such as the recirculation of aconsiderable quantity of the calcine through the column.

In the aforementioned procedure for effecting improved cadmium and leadelimination, the use of less than theory roasting air appeared to beessential even though a solid reducing material such as coal wasintroduced into the upper portion of the column along with the zincsulfide charge. For example, in three similar runs at about 1090 C.,with coal added to. the charge to insure sulfide-volatilizing conditionsin the upper portion of the fluid column, and in which the onlysignificant variation was the proportion of roasting air, 80% of theoryair produced 95% elimination of lead and 99% elimination of cadmium fromthe charge, 90% of theory air produced corresponding eliminations of 92%and 98%, respectively, and 105% of theory air lowered these eliminationsto 53% and 79%, respectively. The sulfide-sulfur contents of thecalcines in these three runs were 4.0%, 1.8% and 0.13%, respectively.

We have now discovered that it is possible to operate a fluid columnroaster for zinc sulfide ore concentrates so as to obtain a calcine lowin residual sulfur while nevertheless achieving the desired eliminationof the cadmium and lead sulfide andother sulfide components of the ore.This result is achieved, pursuant to the present invention, byconcurrently using a substantial excess over theory roasting air and asubstantial amount of 2,855,283 Patented Gct. 7, 1958 fuel gas. Thesubstitution of fuel gas for the solid fuel referred to hereinbeforemakes it possible to use an excess of air, so as to obtain. eflectiveroasting, while nevertheless consuming the excess air so as to maintainnonoxidizing conditions in the upper portion of the fluid column whereinvolatilization of the non-zinciferrous sulinto the lower portion of thefluid bed in an amount at least 5% in excess of that theoreticallyrequired to combine with the zinc sulfide component of the charge, andfuel gas is introduced into the upper portion of the fluid bed asubstantial distance'below the upper surface thereof in amount at leastsufficient to consume the aforesaid excess of sulfide-roasting air andthus provide an atmosphere in the upper portion of the fluid bednon-oxidizing with respect to the sulfides. The sulfide-roasting air andthe fuel gas provide the principal source of the aforementionedfluidizing gas. The fluid bed is maintained at a temperature of at leastabout 900 C., the roasted zinciferous particles are discharged from thelower end of the fluid bed substantially free of the elements whosesufides were volatilized, and roaster gases containing the sulfidesvolatilized from the zinc sulfide charge are withdrawn from the upperend of the fluid bed.

The method of the invention is applicable to the treatment of any zincsulfide ore concentrate containing a significant amount of one or moreof the sufides of cadmium, lead, arsenic, antimony, tin, germanium andmercury. These concentrates are generally obtained by crushing the Zincsulfide ore and subsequently separating and collecting the zinc sulfidecomponent of the ore by flotation methods. The resulting concentrate isin very finely divided form and should be agglomerated into aggregatesor discrete particles of such size that the particles range between 4and 65 mesh (Tyler standard). Within this range of particle size, wehave obtained particularly satisfactory results with particles fallingwithin the range of 6 to 20 mesh. By agglomerating the ore concentrateto particles of this size range, we find that volatilization of thecadmium and lead and roasting of the zinc sulfide can be effectivelyachieved with dustlosses maintained below 30% and generally within therange of 10 to 20%.

The zinc sulfide ore concentrates in fine form may be agglomerated byany suitable procedure. For example, we have obtained whollysatisfactory results by mixing the fine ore concentrate with 2-3% ofbentonite, about 1% sulfite liquor and about 5% water (all percentagesbeing by weight) in a chaser (Chilean) mill for about 20 minutes. Thebentonite contributes strength to the resulting pellets at hightemperature, and the sulfite liquor improves the strength of the pelletswhile still green." The damp mixture was passed through a 6-mesh Rotexscreen moving in a horizontal plane with a gyratory'mot-ion, then onto aconventional disk pelleter. Additional water was sprayed onto the chargeon the pelleting disk during this stage. The resulting pellets weredried in an oven and were then sized through 6 mesh, on 20 mesh Rotexscreen of the type described before. Regardless of whether the discreteparticles of the agglomerated zinc sulfide ore concentrate are formed bythe aforementioned procedure or by any other conventional type ofpelleting technique, the discrete particles of the agglomerated ore'concentrate having the aforementioned size range are amenable to theestablishment of contiguous superimposed volatilizing and roasting fluidbeds pursuant to the invention.

Roasting air is delivered primarily tothe lowermost portion of the fluidcolumn of the charge particles in amount in excess of that theoreticallyrequired tocQmbine with the zinc sulfide component of the charge. Theexcess air is used to obtain complete and prompt elimination of sulfurfrom the zinc sulfide. As the amountof this excess is diminished, theresidual sulfur in the roasted ore tends to increase, but the amount offuel gas needed to consume the unused air is also diminished. As theexcess of air is increased, residual sulfur in the roasted ore tends todecrease and the amount of fuel gas must be increased, resulting in moreheat evolution in the sulfide-volatilization zone. The sulfur dioxideemitted from the roaster also becomes more dilute as the amount ofexcess air is increased. Accordingly, the preferred amount of excess airdepends upon the ore used, the size and condition of the pellets, theamount of residual sulfur which can be tolerated in the roasted ore, thetemperature of operation and the desired composition of the roastergases. In general, we have found that the amount of roasting air shouldbe at least about 5% in excess of that theoretically required to combinewith the zinc sulfide component of the charge and need not be more thanabout 50% in excess of this amount. Within this range, we have found itparticularly advantageous to use about 15 to 35% excess of roasting air,and even within this range the greater the excess air the lower theresidual sulfide and sulfur content of the calcine and the leaner theroaster gases in recoverable sulfur dioxide. Although it is presentlypreferred to introduce all of this roasting air at a single level or attwo vertically spaced levels in the lowermost portion'of the fluidcolumn, we have found that slightly lower residual sulfur contents areobtained when about 5 to of the total roasting air is introduced intothe calcine discharge line immediately below the bottom of the fluidcolumn. With either of these procedures for adding the roasting air, thesimultaneous addition of fuel gas pursuant to the invention insures themaintenance of a non-oxidizing and sulfide-volatilizing zone in theupper portion of the fluid column.

The fuel gas which We have found useful in practicing the invention maybe natural gas, cracking refinery gas or manufactured gas, such asproducer gas or coal gas. It may also consist exclusively or in part ofvaporized fuel oil, obtained by charging fuel oil directly into thefluid column. Accordingly, the term fuel gas as used herein and in theclaims includes both normally gaseous and normally liquid fuels whichare gaseous at the prevailing roasting temperature.

The amount of fuel gas introduced into the fluid col.- umn depends uponthe amount of roasting air supplied to the column. In every instance,however, the amount of fuel gas must be sufiicient to consume in theupper portion of the fluid bed the oxygen of the roasting air unconsumedin the lower portion of the column by the downwardly descending zincsulfide charge. Such an amount of fuel gas will thus establish in theupper portion of the column a gaseous atmosphere substantiallynon-oxidizing with respect to the non-zinciferous sulfides and thuspermit these sulfides to be volatilized as such. However, in order toinsure the maintenance of the aforementioned non-oxidizing conditions inthe sulfide-volatilizing portion of the column, we presently prefer touse a slight excess of fuel gas but less than that which willsignificantly reduce the sulfur dioxide in the exit roaster gases.

The fuel gas is introduced into the fluid column a substantial distancebelow the upper surface thereof, the magnitude of this distance varyingaccording to the geometry of the roasting vessel, but in any event itshould be suflicient to permit the fuel gas to combine with the oxygenin the excess air rising into the upper portion of the charge. The depthof the resulting non-oxidizing Zone in the upper portion of the fluidcolumn determines the retention period of the sulfide charge under thehightemperature volatilizing conditions prevailing therein.

The temperature prevailing in the fluid column is largely determined bythe rate at which the sulfide charge is delivered to the vessel. Thecharge rate should be correlated with the amount of air and fuel gassupplied to the column so as to maintain a bed temperature of about 900to 1100 C., and preferably about 1050-1075 C. Temperatures of at least900 C. appear to be sufficient to obtain adequate elimination of certainof the aforementioned sulfides, provided that a relatively long columnof charge is established so as to maintain a relatively long retentionperiod for the charge in the roasting furnace. With shorter columns, aminimum roasting temperature of about 1000 C. is required. At the otherextreme, temperatures in excess of about 1100 C. (i. e. as high as 1125C.) promote sintering problems in the bed and high dust losses. Wehave'observed that an operating temperature of about 1050-l075 C. iseffective, pursuant to the invention, in eliminating over of the cadmiumand lead sulfides, and similar eliminations of the other non-zinciferoussulfides, in the charge without introducing any serious danger ofsintering of the charge. However, charge sintering can be furtherguarded against, particularly in large cross-section fluid columns whereexcess heat is generated, by immersing water coolers in the bed or byrecirculating through the fluid column some of the calcine dischargedfrom the bottom of the column, or by a combination of these expedients.The amount of recirculated calcine useful for this control over the bedtemperature and sintering tendencies is generally within the range of 10to 25% by weight of the charge of zinc sulfide ore concentrate.

Apparatus suitable for practicing the method of the invention is shownin the single figure of the drawing which is a cross-sectional elevationof the roasting vessel. This vessel comprises a two-section cylindricalvessel, the upper section 1 having an internal diameter substantiallygreater than the lower section 2 and the two sections being joined by aconical intermediate section 3. The roasting vessel is adapted tocontain a column 4 of fluidized charge of the aforementioned discreteparticles in the lower section 2 thereof with this charge extendingupwardly into at least the lower portion of the upper section 1 ofthevessel. The bottom of the lower section 2 of the vessel isadvantageously provided with a conically shaped blow box 5 whichcommunicates with a downwardly extending discharge pipe 6. The lower endof the discharge pipe 6 is provided with a discharge valve 7 whichdelivers the roasted material into the top of a closed discharge hopper8. The roasted material which accumulates in the hopper is dischargedthrough a valve outlet 9. A main air inlet 10 is provided in thelowermost portion of the treating vessel, preferably beneath the conicalblow box 5. Auxiliary air inlets are also advantageously provided, oneof these inlets 11 being positioned a short distance above the main airinlet and the other auxiliary inlet 12 being positioned below the maininlet near the upper end of the discharge pipe 6. A fuel gas inlet 13 isprovided in the upper portion of the lower section 2 of the roastingvessel substantially below the desired level of the upper surface of thefluid column. The uppermost end of the treating vessel is closed with acover plate 14 through which there depends a charge inlet 15 and belowwhich there is also provided a roaster gas outlet 16.

The practice of the invention is illustrated by the following specificoperation. Paragsha zinc sulfide concentrates were used as the chargematerial and contained 46.7% zinc, 32.0% sulfur, 2.1% lead, 0.16%

eadiniuin, 12.6% iron and 0.12% copper. The eoncen trates, which wereabout 80% minus 325 mesh (Tyler standard), were mixed with about 2% ofbentonite, 1% of sulfite liquor and about 5% of water, all percentagesbeing by weight. The mixture was compacted in a chaser mill for about 20minutes, and the resulting damp mixture was passed through a o-m'eshgyratory screen, thence into a conventional disk pelleter. Additionalwater was sprayed onto the charge on the disk pelleter, the resultingpellets were dried in a tray-like oven, and the dry pellets were finallysized to a range of through 6 and on 20 mesh on the aforementionedRoteir gyi'atory'screen.

The roasting was carried 'out'in a furnace such as that shown in thedrawing. The lower cylindrical section 2 of the furnace had a'n internaldiameter of 1 foot and a height of about 3 /2 feet. The conical section3 of the furnace interconnecting the lower cylindrical section with theup er cylindrical section was 11 inches high. The enlarged uppercylindrical section of the furnace had an internal diameter of two feetand a height of about 7 feet. The furnace was charged through the inlet15 with the pellets obtained as described hereinbefere, and the roastedpellets (calcine) passed through the conically shaped blow box 5 at thebottom of the furnaee and into the calcine discharge pipe 6. Thedischarge ipe 6 and the closed discharge hopper 8 effectively sealed oifthe bottom of the vessel so that the amount of roasting air could becarefully measured and controlled. Roasting air was delivered throughthe main inlet 10 immediately below the conical blow box 5 and throughthe auxiliary inlet 11, and this air sup ly effected fluidiza'tion ofthe charge in the furnace. Bottled butane gas was introduced into thefurnace through the inlet 13 positioned about inches below the uppersurface of the fluidized bed. Roaster gases were removed through theoutlet 16, and the cadmium and lead sulfides volatilized from the chargewere separated from the roaster ases, A portion of the roasted charge(the calcine) was recirculated by introducing it into the furnacethrough the charge inlet 15 along with the sulfide charge.

The specific operating data for this roasting operation are given in thefollowing Table I:

T abi I The high elimination of lead and cadmium by the method of ourinvention is clearly apparent from Table 1. Moreover, the sulfur removalfrom the charge is also high, the ratio of 8/8 (sulfide-sulfur) to TotalS (total sulfur) indicates that there was very little sulfate formationduring the roasting operation.

In another run which differed from Run A essentially only in that theroasting air was delivered through the main air inlet 10 and through theauxiliary air inlet 12 below the blow box 5, a still higher cadmium andlead elimination was achieved without significant effect upon the sulfurelimination. The pertinent data for this operation are shown in TableII:

aseaese In still another run pursuant to our invention, the operatingconditions reported for run A were maintained except that a smallproportion of the total roasting air was blown into the discharge hopper8 so that it could ascend the e'a'lcine discharge pipe 6. The result ofthis variation is indicated in Table III, the run being carried out at aperiod when the sulfide-sulfur content of the roasted ore averaged0.70%:

Table III Amount of air to bottom of calcine discharge pipe,Sulfide-sulfur curt min. in calcine,

percent The cadmium and lead eliminations during the variation in airdistribution reported in Table III remained substantially the same as inrun A (Table I).

The method of our invention is applicable to the removal from the zincsulfide ore of any of the volatile sulfides indigenous to the ore. Itwill be readily appreciated that not all Zinc sulfide ores will containsignificant amounts of cadmium, lead, arsenic, antimony, tin, germaniumand mercury sulfides, but any of these sulfides present in the ore willbe largely removed from the zinc sulfide charge in the upper portion ofthe fluid column in the practice of the invention, The thus-volatilizednon-zinciferous sulfides are readily recoverable from the exit roastergases by conventional procedures.

We claim:

1. The method of separating indigenous cadmium, lead, arsenic, antimony,tin, germanium and mercury sulfide components from a finely-divided zincsulfide ore con-.

centrate in a fluid bed roasting operation which com prisesagglomerating the ore concentrate into discrete particles ranging insize between 4 and 65 mesh, charging the agglomerates to the upperportion of a columnar fluid bed of the discrete particles maintained inthe fluidized condition substantially exclusively by the upward flow ofgas, introducing sulfide-roasting air into the lower portion of thefluid bed in amount at least 5% in excess of that theoretically requiredto combine with the zinc sulfide component of the charge, introducinginto the upper portion of the fluid bed but a substantial dis tancebelow the upper surface thereof an amount of fuel gas at leastsuflicient to consume said excess of sulfideroasting air and thusprovide an atmosphere in the upper portion of the fluid bednon-oxidizing with respect to the sulfides, the sulfide-roasting air andthe fuel gas providing the principal source of said fiuidizing gas,maintaining the fluid bed at a temperature of at least about 900 C.,discharging roasted zinciferous particles from the lower end of thefluid bed and withdrawing from the upper end of the fluid bed roastergases containing the sulfides volatilized from the zinc sulfide charge.

2. The method of separating indigenous cadmium,

7 lead, arsenic, antimony, tin, germanium and mercury sulfide componentsfrom a finely-divided zinc sulfide ore concentrate in a fluid bedroasting operation which comprises agglomerating the ore concentrateinto discrete particles ranging in size between 4 and 65 mesh, chargingthe agglomerates to the upper portion of a columnar fluid bed of thediscrete particles maintained in the fluidized condition substantiallyexclusively by the upward flow of gas, introducing sulfide-roasting airinto the lower portion of the fluid bed in amount about 15 to 35% inexcess of that theoretically required to combine with the zinc sulfidecomponent of the charge, introducing into the upper portion of the fluidbed but a substantial distance below the upper surface thereof an amountof fuel gas at least sufficient to consume said excess ofsulfide-roasting air and thus provide an atmosphere in the upper portionof the fluid bed non-oxidizing with respect to the sulfides, thesulfide-roasting air and the fuel gas providing the principal source ofsaid fluidizing gas, maintaining the fluid bed at a temperature of atleast about 900 C., discharging roasted zinciferous particles from thelower end of the fluid bed and withdrawing from the upper end of thefluid bed roaster gases containing the sulfides volatilized from thezinc sulfide charge.

3. The method of separating indigenous cadmium, lead, arsenic, antimony,tin, germanium and mercury sulfide components from a finely-divided zincsulfide ore concentrate in a fluid bed roasting operationwhich'comprises agglomerating the ore concentrate into discreteparticles ranging in size between 4 and 65 mesh, charging theagglomerates to the upper portion of a columnarfluid bed of the discreteparticles maintained in the fluidized condition substantiallyexclusively by the upward flow of gas, introducing sulfide-roasting airinto the lower portion of the fluid bed in amount at least 5% in excessof that theoretically required to combine with. the zinc sulfidecomponent of the charge, introducing into the upper portion of the fluidbed but a substantial distance below the upper surface thereof an amountof butane gas at least sufiicient to consume said excess ofsulfide-roasting air and thus provide an atmosphere in the upper portionof the fluid bed non-oxidizing with respect to the sulfides, thesulfide-roasting air and the fuel gas providing the principal source ofsaid fluidizing gas, maintaining the fluid bed at a temperature of atleast about 900 C., discharging roasted zinciferous particles from thelower end of the fluid bed and withdrawing from the upper end of thefluid bed roaster gases containing the sulfides volatilized from thezinc sulfide charge. 4. The method of separating indigenous cadmium,lead, arsenic, antimony, tin, germanium and mercury sulfide componentsfrom a finely-divided zinc sulfide ore concentrate in a fluid bedroasting operation which comprises agglomerating the ore concentrateinto discrete particles ranging in size between 4 and 65 mesh, chargingthe agglomerates to the upper portion of a columnar fluid bed of thediscrete particles maintained in the fluidized condition substantiallyexclusively by the upward flow of gas, introducing sulfide-roasting airinto the lower portion of the fluid bed in amount at least 5% in excessof that theoretically required to combine with the zinc sulfidecomponent of the charge, introducing into the upper portion of the fluidbed but a substantial distance below the upper surface thereof an amountof fuel oil which when vaporized within the column provides an amount offuel gas at least sufficient to consume said excess of sulfide-roastingair and thus provide an atmosphere in the upper portion of the fluid bednon-oxidizing with respect to the sulfides, the sulfide-roasting air andthe fuel gas providing the principal source of said fluidizing gas,maintaining the fluid bed at a temperature of at least about 900 C.,discharging roasted zinciferous particles from the lower end of thefluid bed and withdrawing. from the upper end of the fluid bed roastergases containing the sulfides volatilized from the zinc sulfide charge.

5. The method of separating indigenous cadmium, lead, arsenic, antimony,tin, germanium and mercury sulfide components from a finely-divided zincsulfide ore concentrate in a fluid bed roasting operation whichcomprises agglomerating the ore concentrate into discrete particlesranging in size between 4 and 65 mesh, charging the agglomerates to theupper portion of a columnar fluid bed of the discrete particlesmaintained in the fluidized condition'substantially exclusively by theupward flow of gas, introducing sulfide-roasting air into the lowerportion of the fluid bed in amount at least 5% in excess of thattheoretically required to combine with the zinc sulfide component of thecharge, introducing into the upper portion of the fluid bed but asubstantial distance below the upper surface thereof an amount of fuelgas at least suff ficient to consume said excess of sulfide-roasting airand thus provide an atmosphere in the upper portion of the fluid bednon-oxidizing with respect tothe sulfides, the sulfide-roasting air andthe fuel gas providing the principal source of said fluidizing gas,maintaining the fluid bed at a temperature of about 1050-1075 C.,discharging roasted zinciferous particles from the lower end of thefluid bed and withdrawing from the upper end of the fluid bed roastergases containing the sulfides volatilized from the zinc sulfide charge.

6. The method of separating indigenous cadmium, lead, arsenic, antimony,tin, germanium and mercury sulfide components from a finely-divided zincsulfide ore concentrate in a fluid bed roasting operation whichcomprises agglomerating the ore concentrate into discrete particlesranging in size between 4 and 65 mesh, charging the agglomerates to theupper portion of a columnar fluid bed of the discrete particlesmaintained in the fluidized condition substantially exclusively by theupward flow of gas, introducing sulfide-roasting air into the lowerportion of the fluid bed in amount at least 5% in excess of thattheoretically required to combine with the zinc sulfide component of thecharge, introducing into the upper portion of the fluid bed but asubstantial distance below the upper surface thereof an amount of fuelgas at least sufficient to consume said excess of sulfide-roasting airand thus provide an atmosphere in the upper portion of the fluid bednon-oxidizing with respect to the sulfides,

the sulfide-roasting air and the fuel gas providing the principal sourceof said fluidizing gas, maintaining the fluid bed at a temperature of atleast about 900 C., discharging roasted zinciferous particles from thelower end of the fluid bed through 'a confined path to an exit valve,introducing a minor portion of said roasting air into the path of theroasted particles in said confined path, and withdrawing from the upperend of the fluid bed roaster gases containing the sulfides volatilizedfrom the zinc sulfide charge.

7. The method of separating indigenous cadmium, lead, arsenic, antimony,tin, germanium and mercury sulfide components from a finely-divided zincsulfide ore concentrate in a fluid bed roasting operation whichcomprises agglomerating the ore concentrate into discrete particlesranging in size between 4 and 65 mesh, charging the agglomerates to theupper portion of a columnar fluid bed of the discrete particlesmaintained in the fluidized condition substantially exclusively by theupward flow of gas, introducing sulfide-roasting air into the lowerportion of the fluid bed in amount at least 5% in excess of thattheoretically required to combine with the zinc sulfide component of thecharge, introducing into the upper portion of the fluid bed but asubstantial distance below the upper surface thereof an amount of fuelgas at least sufficient to consume said excess of sulfide-roasting airand thus provide an atmosphere in the upper portion of the fluid bednon-oxidizing with respect to the sulfides, the sulfide-roasting air andthe fuel gas providing the principal source of said fluidizing gas,maintaining the fluid bed at a temperature of at least about 900 C.,discharging roasted zinciferous particles from the lower end of thefluid bed, withdrawing from the upper end of the fluid bed roaster gasescontaining the sulfides volatilized from the zinc sulfide charge, andseparating from the withdrawn roaster gases the cadmium and leadsulfides volatilized from the zinc sulfide charge in the upper portionof the fluid column.

8. The method of separating indigenous cadmium, lead, arsenic, antimony,tin, germanium and mercury sulfide components from a finely-divided zincsulfide ore concentrate in a fluid bed roasting operation whichcomprises agglomerating the ore concentrate into discrete particlesranging in size between 6 to 20 mesh, charging the agglomerates to theupper portion of a columnar fluid bed of the discrete particlesmaintained in the fluidized condition substantially exclusively by theupward flow of gas, introducing sulfide-roasting air into the lowerportion of the fluid bed in amount at least 5% in excess of thattheoretically required to combine with the zinc sulfide component of thecharge, introducing into the upper portion of the fluid beu out asuostanual distance below the upper surface thereof an amount of fuelgas at least sufficient to consume said excess of sulfide-roasting airand thus provide an atmosphere in the upper portion of the fluid bednon-oxidizing with respect to the sulfides, the sulfide-roasting air andthe fuel gas providing the principal source of said fiuidizing gas,maintaining the fluid bed at a temperature of at least about 900 C.,discharging roasted zinciferous particles from the lower end of thefluid bed and withdrawing from the upper end of the fluid bed roastergases containing the sulfides volatilized from the zinc sulfide charge.

References Cited in the file of this patent UNITED STATES PATENTS303,456 Rae Aug. 12, 1884 414,051 Hutchinson Oct. 29, 1889 2,596,580McKay et al. May 13, 1952 2,621,118 Cyr et al. Dec. 9, 1952 2,650,159Tarr et al. Aug. 25, 1953 2,789,034 Swaine et al. Apr. 16, 1957

1. THE METHOD OF SEPARATING INDIGENOUS CADMIUM, LEAD, ARSENIC, ANTIMONY,TIN, GERMANIUM AND MERCURY SULFIDE COMPONENTS FROM A FINELY-DIVIDED ZINCSULFIDE ORE CONCENTRATE IN A FLUID BED ROASTING OPERATION WHICHCOMPRISES AGGLOMERATING THE ORE CONCENTRATE INTO DISCRETE PARTICLESRANGING IN SIZE BETWEEN 4 AND 65 MESH, CHARGING THE AGGLOMERATES TO THEUPPER PORTION OF A COLUMNAR FLUID BED OF THE DISCRETE PARTICLESMAINTAINING IN THE FLUIDIZED CONDITION SUBSTANTIALLY EXCLUSIVELY BY THEUPWARD FLOW OF GAS, INTRODUCING SULFIDE-ROASTING AIR INTO THE LOWERPORTION OF THE FLUID BED IN AMOUNT AT LEAST 5% IN EXCESS OF THATTHEORETICALLY REQUIRED TO COMBINE WITH THE ZINC SULFIDE COMPONENT OF THECHARGE, INTRODUCING INTO THE UPPER PORTION OF THE FLUID BED BYT ASUBSTANTIAL DISTANCE BELOW THE UPPER SURFACE THEREOF AN AMOUNT OF FUELGAS AT LEAST SUFFICIENT TO CONSUME SAID EXCESS OF SULFIDEROASTING AIRAND THUS PROVIDE AN ATMOSPHERE IN THE UPPER PORTION OF THE FLUID BEDNON-OXIDIZING WITH RESPECT TO THE SULFIDES, THE SULFIDE-ROASTING AIR ANDTHE FUEL GAS PROVIDING THE PRINCIPAL SOURCE OF SAID FLUIDIZING GAS,MAINTAINING THE FLUID BED AT A TEMPERATURE OF AT LEAST ABOUT 900* C.,DISCHARGING ROASTED ZINCIFEROUS PARTICLES FROM THE LOWER END OF THEFLUID BED AND WITHDRAWING FROM THE UPPER END OF THE FLUID BED ROASTERGASES CONTAINING THE SULFIDES VOLATILIZED FROM THE ZINC SULFIDE CHARGE.